1. Lab-Gravity Notes-Forces of Gravity Video
TODAY:
Lab-Gravity
Notes-Forces of Gravity
Video

2. What is gravity? Gravity:
is the force that pulls things toward the Earth.
exists between two objects that have mass
Gravitation:
Is a force that acts between all masses and causes them to attract one another.
The larger and closer the two masses, the more gravitation affects them
Eg. holds the moon in its orbit around the Earth
Eg. holds Earth in its orbit around the sun

3. Mass, Force and Gravity
Mass – Amount of stuff (atoms/molecules) in an object. Measured in kg.
Force – Measures the gravitational pull on something. Measured in N (newtons)
Earths Gravitational Field Strength – 10N/kg. (The gravitational field strength at the surface of the Earth produces a force of approximately N on every mass of 1 kg)

4. Gravitational field:
Sun’s gravitational force makes the Earth move in an orbit around the Sun.
Earth’s gravitational force makes the ball move down towards the centre of the Earth.

5. Putting it all together
The apple has mass (kg).
It gets pulled to the ground at a force (this can be measured in Newtons)
The earth’s gravitational field strength pulls the apple towards it.

6. Now… Weight Hang on a minute…that sounds very familiar… Weight = Force
Is the gravitational force acting on an object.
A measure of force pulling something to the ground due to gravity.
Hang on a minute…that sounds very familiar…
Weight = Force
Weight is measured in N (newtons)

7. Putting it all together
The apple has mass (kg)
It gets pulled to the ground at a force (this can be measured in Newtons) = WEIGHT
The earth’s gravitational field strength pulls the apple towards it

8. How can we calculate weight?
We can use an equation we already know to help us:
g (gravitational field strength) = force / mass
If Force = Weight
Weight = Mass x g (gravitational field strength)
Memorise: W = m X g

9. Air Resistence:
The force of air pushing on an object as the object moves through the air.
Eg fluid friction
Eg airplane flies through the air hitting particles